Today many types of component mounting machines exist. However, the ones relevant for the present invention are those initially defined, i.e. those where the boards are provided from cassettes. A prior art machine of this kind has an input cassette and an output cassette for carrying unprocessed boards, i.e. boards which are to be provided with components, and processed boards, i.e. boards on which components have been placed, respectively. In operation a board is fetched from the input cassette and placed on the board carrier. Then the board carrier is moved along a first axis, or y-axis and the mounting head is moved along a second axis, or x-axis perpendicular to the first axis, for positioning the mounting head relative to the board, while components are mounted on the board. Finally, the thus processed board on the carrier is put to the output cassette and another unprocessed board is placed on the carrier. When the input cassette is empty, and, consequently, the output cassette is full, an operator replaces those cassettes with new ones. There are other principles for the very mounting of the components, such as fixing the board on the carrier and then moving the mounting head in both x and y directions, or moving only the carrier both in x and y directions. Before continuing to discuss this prior art, a few definitions are to be made for the purposes of this application. By “board” is meant any carrier on which components can be mounted. By “component” is meant an electronic element, which can be mounted on a board. By “mount” is meant to pick a component and place it on a board. Within the technical field of this invention one type of relevant component mounting machine is often called a pick and place machine.
Since the size of a cassette, i.e. the number of boards that it can hold, is more or less standardised and relatively limited, the time used by the operator to exchange the cassettes is substantial relative to the useful time for mounting components on all boards held in a cassette. This also causes a substantial idle time for the machine, during which it is unproductive. Of course it would be impossible to increase the height of a cassette towards infinity in order to decrease the idle time per board. Further, the number of operator interventions per time period is high. These problems are larger the smaller the number of components mounted on each board is.
A prior art effort to solve the above stated problems, consists of a board handling apparatus which comprises a loader for providing boards to a component mounting machine and an unloader for fetching boards from the machine. Each one of said loader and unloader has an upper cassette holder, a lower cassette holder, each one thereof holding a plurality of cassettes, and an elevator device. An input cassette is fetched from the upper cassette holder, placed on the elevator device, and positioned for loading boards. For each board which is removed from the input cassette the cassette is lowered one step. When the input cassette is empty it is further lowered, and put into the lower cassette holder, while another full input cassette is positioned for loading boards. Alternatively the elevator is raised step-by-step while loading boards.
However, while reducing the problems discussed above, this prior art solution adds other problems. One major problem is that it adds a substantial degree of complexity by introducing a mechanism for moving the cassettes horizontally between the cassette holders and the elevator device. Further, the board handling apparatus requires a substantial amount of space.